Frequency synchronizing system



April 25, 1950 E. H. HUGENHOLTZ ETAL 2,505,543

FREQUENCY SYNCHRONIZING SYSTEM Filed July 20, 1946 2 Sheets-Sheet 1EDUARD HERMANHUGEMJULTZ BONIFACIUS JOHANNES WIZARDHVBURG I N V EN TORS.

AGENT.

April 25', 1950' E. H. HUGENHOLTZ ET AL 2,505,642

FREQUENCY SYNCHRONIZING SYSTEM Filed July 20,1946 2 Sheets-Sheet 2 MOTORDIRECTION CONTROL EDUARD HERMAN H UGENHOLT Z B ONZEACJ US JOHANNESVANHARDENB UB6,

I N VEN TORS AGENT l atented Apr. 25, 1950 FREQUENCY SYNOHRONIZINGSYSTEM Eduard Herman Hugenholtz and- Bonifacius Johannes van Hardenberg,Eindhoven, Netherlands, assignors to, Hartford National Bank'and TrustCompany, Hartford, Conn-., as trustee Application July 20, 1946,Serial'No. 685,123 In the Netherlands December 3, 1943 Sectionl, Public:Law 690,.August 8, 1946 Patent: expires December 3, 1963 8 Claims;

This invention relates to a circuit-arrangement' for comparingand/or forcontrolling to equality the frequencies of two electrical oscillations.

According to the invention, from the, said oscill'ations are derived atleast two voltagesof the differential frequency (anauxiliary voltage andan adjusting voltage) which have different phases. These voltagesaresupplied to a device which-so long as the said frequencies areunequal--is alternately released and switched off by the said auxiliaryvoltage and which at the moment of'release selects one of twoconditions. of stable equilibrium depending upon the instantaneousdirection of the said adjustingwoltage, thisdirection being determinedby the sign of the frequency difference between the two frequencies,whereas in the case of inequality of the frequencies the device isswitched off by the auxiliary voltage assoon as the phase differencebetween. the. two oscillations drops below a determined value. From thesaid device are taken one or'more output voltages (and/or outputcurrents) with the aid of which the comparison and/or the control of thefrequencies are effected.

By means of the well-known circuit-arrangements for the automaticfrequency-control the frequencies of two' oscillations can, in general,

be made only approximately equal to one. an.-

other; The'circuit-arrangement accordingt'o the invention, on thecontrary, offers the advantage that the frequencies of the twooscillations can be controlled to synchronism in'a simplemanner. Thecircuit-arrangement according to the invention exhibits furthermore theadvantage that theoperation is independent of the absoluteval ues'of thefrequencies to be compared or controlled but depends solelyon'the'frequency difference of the oscillations (of course with" the exceptionof that part of the" circuit-arrangement which generates the twovoltages of the differential frequency); The circuit-arrangement mayalso'be adjusted in such manner that in casewof the suppression of oneof the'oscilla tions' the said device is switchedoff so that the controlis not disturbed. A very'important advantage is furthermore that thecontrol 'tosyrrchronismis independent of. the circuit elements used;more particularly. of the properties of the r discharge systems used.

Care should preferably be'taken to insure that the voltage of'the.differential frequency; exhibit amutualphas'e difference of 90;

Particularlysatisfactory results are obtained i 2. if the said deviceconsistsof at least two discharge tubes each of which comprises, besidesan anode, a cathode and a control grid, at least one-additional grid,whilst. the anodeof each of the tubes isconnected to the control grid ofthe other tube, the said additional grids being directly connected tooneanother. Inthis case't'he adjusting. voltage is preferably supplied inantiphase to the control grids whilst the auxiliary voltage, whichalternately releases and switches off the discharge tubes, is suppliedto the directly interconnected grids.

The said device may also consist of at least two discharge tubes inwhich the adjusting voltage and: the auxiliary voltage are both suppliedto the control grids of these discharge tubes, the auxiliary voltagebeing supplied to the control gridsin the same phase and the adjustingvoltage beingsuppliedthereto in anti-phase.

In further embodiment of the invention the said device consists of adischarge tube comprising, an anodeacathode and at least three grids,the adjusting voltage and the auxiliary voltage being supplied to thefirst grid and to the third grid respectively. A positive feed-back isprovided' between the third and second grids and the output voltages oroutput currents serving for the control or for the comparison, are takenfrom. the anode and from the second grid.

In order that the invention may be clearly understood andreadily carriedinto effect, it will now be explained with reference to the accompanyingdrawing, in which Fig. 1 represents, by way of example, one embodimentof the invention. Fig.12'shows the variation of the voltages of thedifferential" frequency which are derived from the saidpscillations;these voltages have a mutual'phase'difference of 90. Fig. 3 represents"a mechanical and a cooperating electric control device coupled to thecircuit-arrangementshown in Fig; 1.

In the circuit-arrangement shown in Fig. 1 the'said oscillations, whosefrequencies are f1 and f2 respectively, are supplied to terminals l and2" respectively. The oscillations of the frequency fl aretransferred viathe secondary windings 3 and :1 respectively of a transformer 5 tomixing stages 6" and '7 respectively'which pertain to the circuitarrangem'ent. Theoscillations of the'frequency. f2 are supplied to aphase-rotating network fl, which consists of two resistancesand twocapacities which are included in a bridge circuit. From this network aretaken two voltages which have both the frequency hand which exhibit amutualpha'se difference of 90; one of these voltages is supplied to themixing stage 6 and the other to the mixing stage I.

The mixing stages 6 and I comprise each two detectors I3, I3" and I4,I4" respectively which are connected in opposition to one another, sothat the direct current voltage components appearing during the mixingoperation counterbalance each other at least partly.

By mixing the voltages of the frequencies f1 and is a voltage of thedifferential frequency (fa-J1) is produced in each of the mixing stages6 and "i, these voltages having a phase difference of 90. They are takenfrom the output resistance 9 and I respectively and are supplied to thepreviosuly mentioned device which has two conditions of stableequilibrium.

This device is composed of two discharge tubes II and i2, which areconstructed as pentodes whose respective cathodes, anodes and screengrids are connected to one another.

The voltage of the differential frequency which is produced in themixing stage 6 and which is used as the auxiliary voltage is appliedbetween the suppressor grids and the earthed cathodes of the twopentodes I I and I2. In addition, a source of direct-current voltage Iis connected in series with this voltage.

The voltage of the differential frequency which is produced in themixing stage i and which acts as the adjusting voltage is supplied inantiphase to the control grids of the discharge tubes II and I2. To thatend there is connected to the output terminals of the mixing circuit 1 aresistance It, whose mid-point is connected through a source ofdirect-current voltage I! to the cathodes of the discharge tubes. Theends of the resistance It are connected through a resistance I8 to thecontrol grid of the tube II and through a resistance I9 to the controlgrid of the tube I2. The control grid of the discharge tube II isconnected through a resistance 29 to the anode of the discharge tube I2and the com trol grid of the tube I2 is connected through a resistance2| to the anode of the tube II.

In the anode circuit of the discharge tube II are connected in series aresistance 22 and the exciting winding of a relay 23. The anode circuitof the tube I2 likewise comprises a resistance 24 connected in serieswith the exciting winding of a relay 25. The screen grids of thedischarge tubes are directly connected to a source of anodedirect-current voltage (not shown).

The operation of the circuit-arrangement may be explained as follows:

The device consisting of the two pentodes has two conditions of stableequilibrium; in the one condition the pentode II carries current and thepentode I 2 is blocked; in the other condition just the contrary is thecase. With the aid of the voltage of the differential frequency whichoriginates from the mixing stage 6 the two discharge tubes arealternately conducting and non-conducting at any rate as long as thefrequencies to be compared are unequal. The point at which the pentodesbecome conducting due to a positive value of the auxiliary voltage isdetermined inter alia by the bias voltage originating from the source ofdirect-current voltage l5. Let us assume that this bias voltage isadjusted in such a manner that at the said point the auxiliary voltagehas the value zero so that the said point corresponds to the point P inFig. 2a which shows the variation of the auxiliary voltage. Fig. 2bshows the variation of the adjusting voltage. This voltage has a phasedifference of 90 with respect to the auxiliary voltage and itconsequently has its maximum positive or negative value at the moment(point P) when the auxiliary voltage has the zero value. The adjustingvoltage is assumed to have at this moment its maximum positive value ifI2 is higher than f1 (curve I) and its maximum negative value if I1 ishigher than f2 (curve 11).

At the moment when the device is released by the auxiliary voltage, thecontrol grid of the pentode II is made more positive and at the sametime the control grid of the pentode I2 more negative or converselyaccording as i2 is higher or lower than ii.

The device being once released, the auxiliary voltage has no longer anyinfluence on the operation of the circuit-arrangement, until the momentwhen the auxiliary voltage has become again sufficiently negative toswitch off the device. The behaviour of the device, i. e. the choice ofone of the two conditions of equilibrium after the release isconsequently solely determined by the direction of the adjustingvoltage, provided that this voltage-remaining within determinedlimitsexceeds a determined value in that direction. Now if is is higherthan if, the control grid of the pentode II is at the moment of release,according to the example given above, more positive than the controlgrid of the pentode I 2, with the result that the device is in thatcondition of equilibrium in which the pentode II carries current and thepentode I2 is blocked. This position is maintained until the whole ofthe device is switched off again by the auxiliary voltage. As long as isis higher than if this is repeated, the pentode i I alternately carryingcurrent and being blocked and the pentode I2 remains permanentlyblocked. In the time interval in which the pentode I i carries current,the relay 23 is excited, which may result, for example, in switching ona motor 43 coupled to a motor direction control &2 (see Fig. 3) by whichthe frequency I1 is increased. Alternatively the frequency )2 may bedecreased or both frequencies can be simultaneously adjusted tosynchronism. Motor direction control 52 and motor 43 may be any one ofthe well-known combinations for performing the above-described function.

The relay 25 is excited in a similar manner if the frequency i2 is lowerthan ii, in which event the frequency I2 is raised and/or the frequency)1 is reduced.

This control continues until the frequencies f1 and f2 are equal, inwhich event the mixing stages 6 and 'I yield a direct-current voltagewhose value and direction depend on the phase difference between the twofrequencies to be compared. Now the circuit adjusts itself in such amanner that the auxiliary voltage (see Fig. 2a) becomes negative andremains so, for if this voltage acquires a positive value, the twodischarge tubes are permanenty released and one of the two continuouslycarries current. Owing to this either of the relays 23 and 25 iscontinuously excited and the motor control is put into operation withthe result that the phase difference between the oscillations is changedand this until the said direct-current voltage becomes nil or takes anegative value. Then the two discharge tubes are permanently switchedoff, the motor control remains inoperative and the frequencies f1 and f2remain equal to one another. The phase difference between thesefrequencies may vary within a range of approximately without the devicebeing put into operation. This range approximately corresponds to, therange within which the auxiliary; voltage 1 is. negative (see, Fi 2a) Ifthe phase between the. two oscillations;

changes, the auxiliary voltage finally becomes again positive; ifthephase changes in theone.

pentode begins to carry current owing to the,

influence of the adjusting. voltage, which has obtained now just theopposite sign. Within the range of approximately 180 inwhich theauxiliary voltage is negativethe circuit consequently does not reacttophase-differences between the initial oscillations, whereas in thecaseof larger phase divergencesthecontrol becomes operative and, correctsthese divergences.

The, above-described control of the. frequency of one of theoscillations or of; the frequencies of both oscillations, which issolely effected by means of a mechanical control device (in the presentcase a motor) may efiiciently be combined with a control of one of thefrequencies or of both frequencies by an electric agency. Fig. 3represents a circuit-arrangement relating to such a control. Thiscircuit-arrangement may, for example, be connected. to the adjustingvoltage (see, Fig. 2b), This voltage, which may be taken from the mixingstage E of the circuit-arrangement according to Fig. 1, is supplied tothe terminals denoted by 26 in the figure.

The oscillatory circuit of the oscillator whose frequency; has to bereadjusted (for example, the oscillator which generates the frequencyfl) is diagrammatically shown in the figure at 21. This oscillatorycircuit has connected in parallel with it two branches is and 29, the.former consisting of the series-connection of a diode 30, a condenser3.l and aseparating condenser 32 and the latter being constituted by theseries-connection of a diode 33, which has a, condenser 34 con nected inparallel with it, a resistance 35 and two separating condensers36 and31. One of the terminals 26 is connected through a resistance 4| to theanode of the diode. 30 and through a resistance 38 to the cathode of thediode 33 whereas.

the other terminal is. connected through a resistance 39 to the cathodeof the diode 3i] and through aresistance 40 to the anode of the diode.

The cathodes of the two diodes are interof the diode 3B is positive withrespect to the.

other terminal, the diode 30 becomes conductive, whereas the. diode 33is blocked with the result that. the capacitative effect of the branch28 is increased andv the. value of the capacity con: nected in parallelwith the oscillator circuit 21 increases. If, on the contrary, the otherterminalbecomes positive, the diode 33 becomes conductive and. the.diode 30 is blocked. The consequence thereof is that the condenser 34 isshortscribed, has ensured that the two oscillations,

have approximately attained thepoint of synchronism.

The above-described additional control by electric means is importantbecauseby means. of a,

mechanical control devicealone-itzis in general not well possible, dueto the inertia present, to. obtain a stable control. The describedmechani-- cal control, however, offers the advantage that upon thesuppression of one of the oscillations the already obtained controltofrequency equality is not afiected.

The electric control may be connected not only to the adjusting voltagebut also, for example,- to the difference between the anode voltages ofthe discharge tubes I l and 12.

It is also possible to control the oscillationsby electric agency tofrequency. equality, that is to say by connecting the discharge tubes Hand 42 in such a manner that they act as reactances depending on themutual conductance.

What we claim is:

1. A circuit arrangement for comparing and equalizing the frequency oftwo electric oscillations, comprising means to produce a first voltageof frequency proportional to the difference in frequency between saidtwo electric oscillations, means to produce a second voltage offrequency proportional to said difference in frequency between said twoelectric oscillationsand displaced; in phase with respect to said firstvoltage, a circuit comprising a first electriccurrent path and a. secondelectric current path, means responsive to. said first voltage tocyclically open and close said electric current paths, means responsiveto said second voltage to select one of said electric current pathsduring the period when said pa as are open and to cause a current fiowtherein, the electric current path selected depending on the directionof the difference in frequency between said electric oscillations, meansresponsive to current flow in said first electric current path to varythe frequency of oneof said electric oscil-. lations in a givendirection, means responsive to. current flow in said second electriccurrent path to vary the frequency of said electric oscillation theopposite direction, and means to close both of said paths when saiddifierence in frequency of said electric oscillations is equal to zero.

2. A circuit arrangement for comparing and. equalizing the frequency oftwo electric oscillations, comprising-means to produce a first voltageof frequency proportional to the difference in frequency between saidtwo electric oscillations. means to produce a second voltage offrequency proportional to said difference in frequency be-. tween saidtwo electric oscillations and dise placed out of phase with respect tosaidfirst voltage, a circuit comprising a. first electric cur-. rentpath and a second electric current path, means responsive to said f rstvoltage to cycli cally open and close said electric current paths,

means responsive to said second voltage to select one of said electriccurrent paths during the period when said paths are open and to cause acurrent flow therein, the electric current path selected depending onthe direction of the difference in frequency between said electricoscillations, means responsive to current flow in said first electriccurrent path to vary the frequency of one of said electric oscillationsin a given direction, means responsive to current flow in said secondelectric current path to vary the frequency of said electric oscillationin the opposite direction, and means to close both of said paths whensaid difference in frequency of said electric oscillations is equal tozero.

3. A circuit arrangement for comparing and equalizing the frequency oftwo electric oscillations, comprising means to produce a first voltageof frequency proportional to the difference in frequency between saidtwo electric oscillations, means to produce a second voltage offrequency proportional to said difference in frequency between said twoelectric oscillations and being 90 out of phase with respect to saidfirst voltage, a first and a second electron discharge tube having acathode, a control grid, a further grid and an anode, means to couplethe anode of said first tube to the control grid of said second tube andmeans to couple the anode of said second tube to the control grid ofsaid first tube to block said second tube when ,said first tube isconducting and conversely to block said first tube when said second tubeis vcomiucting, means to apply said first voltage in phase to saidfurther grids of said first and said second electron discharge tubes tocyclically hold and release said tubes, means to apply said second-voltage in anti-phase to the control grids of :said first and saidsecond electron discharge tubes to render one of said tubes conductingduring the period when said tubes are released, the one of said tubesselected depending on the relative direction of the difference infrequency, means responsive to current fiow in said first tube to varythe frequency of one of said oscillations in a given direction, meansresponsive to current fiow in said second tube to vary the frequency ofsaid one of said oscillations in the opposite direction, and means toblock said electron discharge tubes when the difference in frequency ofsaid electric oscillations is equal to zero.

4. A circuit arrangement for comparing and equalizing the frequency oftwo electric oscillations, comprising means to produce a first voltageof frequency proportional to the difference in frequency between saidtwo electric oscillations, means to produce a second voltage offrequency proportional to said difference in frequency between said twoelectric oscillations and being 90 out of phase with respect to saidfirst voltage, a first and a second electron discharge tube having acathode, a grid and an anode, means to couple the anode of said firsttube to the grid of said second tube, means to couple the anode of saidsecond tube to the grid of said first tube to block said second tubewhen said first tube is conducting and conversely to block said firsttube when said second tube is conducting, means to apply said firstvoltage in phase to said grids of said first and said second electrondischarge tubes to cyclically hold and release said tubes, means toapply said second voltage in anti-phase to the grids of said first andsaid second electron discharge tubes to render one of said tubesconducting during the period when said tubes are released the one ofsaid tubes selected depending on the relative direction of thedifference in frequency, means responsive to current flow in said firsttube to vary the frequency of one of said oscillations in a givendirection, means responsive to current flow in said second tube to varythe frequency of said one of said oscillations in the oppositedirection, and means to block said electron discharge tubes when thedifierence in frequency of said oscillations is equal to zero.

5. A circuit arrangement for comparing and equalizin the frequency oftwo electric oscillations, comprising means to produce a first voltageof frequency proportional to the difference in frequency between saidtwo electric oscillations, means to produce a second voltage offrequency proportional to said difference in frequency between said twoelectric oscillations and being out of phase with respect to said firstvoltage, a first and a second electron discharge tube having a cathode,a control grid, a screen grid, a further grid and an anode, means tocouple the anode of said first tube to the control grid of said secondtube, means to couple the anode of said second tube to the control gridof said first tube to block said second tube when said first tube isconducting and conversely to block said first tube when said second tubeis conducting, means to apply said first voltage in phase to saidfurther grids of said first and said second electron discharge tubes tocyclically hold and release said tubes, means to apply said secondvoltage in antiphase to the control grids of said first and said secondelectron discharge tubes to render one of said tubes conducting duringthe period when said tubes are released depending on the relativedirection of the difference in frequency, means coupled to the anode andscreen grid of said first tube to vary the frequency of one of saidoscillations in a given direction, means coupled to the anode and screengrid of said second tube to vary the frequency of said one of saidoscillations in the opposite direction, and means to block said electrondischarge tubes when the difference in frequency of said oscillations isequal to zero.

6. A circuit arrangement for comparing and equalizing the frequency oftwo electric oscillations, comprising means to produce a first voltageof frequency proportional to the difference in frequency between saidtwo electric oscillations, means to produce a second voltage offrequency proportional to said difference in frequency between said twoelectric oscillations and being 90 out of phase with respect to saidfirst voltage, a first and a second electron discharge tube having acathode, a control grid, a further grid and an anode, means to couplethe anode of said first tube to the control grid of said second tube,means to couple the anode of said second tube to the control grid ofsaid first tube to block said second tube when said first tube isconducting and conversely to block said first tube when said second tubeis conducting, means to apply said first voltage in phase to saidfurther grids of said first and said second electron discharge tubes tocyclically hold and release said tubes, means to apply said secondvoltage in anti-phase to the control grids of said first and said secondelectron discharge tubes to render one of said tubes con ducting duringthe period when said tubes are released depending on the relativedirection of the difference in frequency, a first relay responsive tocurrent flow in said first tube, mechanical means actuated by said firstrelay to vary the frequency of one of said oscillations in a givendirection, a second relay responsive to current flow in said secondtube, mechanical means actuated by said second relay to vary thefrequency of said one of said oscillations in the opposite direction,and means to block said electron discharge tubes when the difference infrequency of said oscillations is equal to zero.

7. A circuit arrangement for comparing and equalizing the frequency oftwo electric oscillations, comprising means to produce a first voltageof frequency proportional to the difference in frequency between saidtwo electric oscillations, means to produce a second voltage offrequency proportional to said difference in frequency between said twoelectric oscillations and being 96 out of phase with respect to saidfirst voltage, a first and a second electron discharge tube having acathode, a control grid, a further grid and an anode, means to couplethe anode of said first tube to the control grid of said second tube,means to couple the anode of said second tube to the control grid ofsaid first tube to block said second tube when said first tube isconducting and con versely to block said first tube when said secondtube is conducting, means to apply said first voltage in phase to saidfurther grids of said first and said second electron discharge tubes tocyclically hold and release said tubes, means to apply said secondvoltage in anti-phase to the control grids of said first and said secondelectron discharge tubes to render one of said tubes conducting duringthe period when said tubes are released depending on the relativedirection of the difference in frequency, a first relay responsive tocurrent flow in said first tube, mechanical means actuated by said firstrelay to vary the frequency of one of said oscillations in a givendirection, a second relay responsive to current flow in said secondtube, mechanical means actuated by said second relay to vary thefrequency of said one of said oscillations in the opposite direction,electrical means responsive to a voltage of frequency proportional tothe difference in frequency of said electric oscillations to vary thefrequency of said one of said electric oscillations over a range offrequencies in the proximity of synchronism of said electricoscillations, and means to block said electron discharge tubes when thedifference in frequency of said oscillations is equal to zero.

8. A circuit arrangement for comparing and equalizing the frequency oftwo electric oscillations, comprising means to produce a first voltageof frequency proportional to the difference in frequency between saidtwo electric oscillations, means to produce a second voltage offrequency proportional to said difference in frequency between said twoelectric oscillations and being 90 out of phase with respect to saidfirst voltage, a first and a second electron discharge tube having acathode, a control grid, a further grid and an anode, means to couplethe anode of said first tube to the control grid of said second tube,

19 means to couple the anode of said second tube to the control grid ofsaid first tube to block said second tube when said first tube isconducting and conversely to block said first tube when said second tubeis conducting, means to apply said first voltage in phase to saidfurther grids of said first and said second electron discharge tubes tocyclically hold and release said tubes, means to apply said secondvoltage in anti-phase to the control grids of said first and said secondelectron discharge tubes to render one of said tubes conducting duringthe period when said tubes are released depending on the relativedirection of the difference in frequency, a first relay responsive tocurrent fiow in said first tube, mechanical means actuated by said firstrelay to vary the frequency of one of said oscillations in a givendirection, a second relay responsive to current flow in said secondtube, mechanical means actuated by said second relay to vary thefrequency of said one of said oscillations in the opposite direction, athird and a fourth electron discharge tube having an anode and acathode, a first capacitor and a second capacitor, means to couple saidfirst capacitor in series with said third electron discharge tube acrossthe frequency-determining circuit of said one of said electricoscillations, means to couple said second capacitor in series with saidthird electron discharge tube across said frequency-determining circuit,the resultant reactance of the capacity of said first capacitor and theinternal resistance of said third electron discharge tube having a valueat which the frequency of said one of said oscillations is varied insaid given direction over a range of frequencies in the proximity ofsynchronism of said electric oscillations, and the reactance of thecapacity of said second capacitor and the internal resistance of saidfourth electron discharge tube having a value at which the frequency ofsaid one of said oscillations is varied over said range of frequenciesin said opposite direction, means responsive to said second voltage torender one of said third and fourth electron discharge tubes conductingto vary the frequency of said one of said oscillations in thecorresponding direction, and means to block said electron dischargetubes when the diiTerenCe in frequency of said oscillations is equal tozero.

EDUARD HERMAN HUGENHOLTZ. BONIFACIUS JOHANNES VAN HARDENBERG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,104,801 Hansell Jan. 11, 19382,221,517 Holters Nov. 12, 1940 2,225.348 Mikelson Dec, 17, 19402,302,123 Hepp Nov. 17, 1942 2,408,451 Sorensen Oct. 1, 1946

